Apparatus for and method of de-waxing, presintering and sintering powdered metal compacts

ABSTRACT

In this apparatus a de-waxing operation is performed in hydrogen, and the same vessel is used for vacuum sintering without moving of the part to be heat treated, and in one continuous operation.

United States Patent [15] 3,654,374 Scheyer [4 1 Apr. 4, 1972 [54] APPARATUS FOR AND METHOD OF [56] References Cited DE-WAXING, PRESINTERING AND UNITED STATES PATENTS SINTERING POWDERED METAL P T 3,257,492 6/1966 Westeren ..l3/3l COM AC 8 3,361,864 1/1968 Vollmer et al. ..l3/31 X [72] Inventor: Gerard Scheyer, Morris Plains, NJ.

. Primary Examiner-Bernard A. Gilheany [73] Assignee. IAldlumns Carbide Corporation, Kemlworth, Assistant Emminer R. N. Ema, Jr

Attorney-J. B. Felshin [22] Filed: July 25, 1969 57 ABSTRA T [2]] Appl. No.: 844,972 l C In this apparatus a de-waxing operation is performed in hydrogen, and the same vessel is used for vacuum sintering US. ith t i g f th p t t b h t t t d, d i one [51] Int. Cl. tinuous operation. [58] Field of Search ..l3/31, 20

19 Claims, 5 Drawing Figures DRAIN INLET PATENTEDAPR 41972 3, 654, 374

SHEET 1 or 3 a0 F/G/ INVENTOR.

GERARD SCHEYER PATENTEDAPR 419 72 SHEET 2 0F 3 INVI'JNI'UR. GERARD SCHEYER 3 ATTORNEY PATENTEDAPR 41972 sum 3 OF 3 l iY 6 05 K) ATI'URNICY APPARATUS FOR AND METHOD OF DE-WAXING, PRESINTERING AND SINTERING POWDERED METAL COMPACTS BACKGROUND OF THE INVENTION SUMMARY OF THE INVENTION An object of this invention is to provide a highly improved I apparatus of the character described in which the de-waxing in hydrogen and sintering in vacuum is combined in a single vessel without transfer of the compact from the vessel.

Another object of this invention is to provide a highly improved process of the character described comprising placing compacts in a pot which is placed inside of a chamber; feeding hydrogen to the pot and feeding argon to the chamber; applying heat to the chamber so that the waxes in the compacts are volatalized and carried off through a removable graphite chimney communicating with the pot, the argon protecting the graphite components from oxidizing and excluding the air, then flushing out the hydrogen from the pot with argon, removing the chimney, placing a sight glass over the chimney opening, stopping all the gas flow and pumping out all gas from the chamber and pot to produce a vacuum and bringing up the heat to sinter the compacts in vacuum.

Yet another object of this invention is to provide in apparatus of the character described, a highly improved cooled port through which the graphite chimney passes, to keep the graphite cool and stop it from oxidizing, and under vacuum operation when the graphite chimney has been removed and a sight glass has been installed, to prevent clouding up of the sight glass by preventing condensible vapors to settle on the sight glass.

Still another object of this invention is to provide a relatively inexpensive apparatus of the character described which shall be economical to operate and which shall yet be practical and efficient to a high degree.

Other objects of this invention will part hereinafter pointed out.

The invention accordingly consists in the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the construction hereinafter described, and of which the scope of invention will be indicated in the following claims. The invention also consists in steps of a process hereinafter described.

in part be obvious and in BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a vertical axial cross-sectional view of apparatus embodying the invention and showing the position of the parts during the de-waxing operation;

FIG. 2 is a cross-sectional view taken on line 22 ofFIG. 1;

FIG. 3 is a cross-sectional view taken on line 3-3 ofFIG. 1;

FIG. 4 is a vertical cross-sectional view of the upper portion of the apparatus shown in FIG. 1 with the graphite chimney removed, the sight glass mounted on the cooled port and the swinging graphite sight hole disc or plate moved to center sight hole with the hole in the lid of the inner part; and

FIG. 5 is a piping diagram.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now in detail to the drawing, designates apparatus embodying the invention. Said apparatus comprises an outer container 11 having an outer cylindrical wall 12 and a circular bottom wall 13 formed with a central hole 14. Within said container 11 is a circular inner bottom wall 15 spaced above wall 13. Mounted on wall 15 is an inner cylindrical wall 16. Between walls 12, 16 and 13,15 is a waterjacket 17 closed at its upper end by a ring 18. A water inlet pipe 19 leads to the upper end of the jacket 17.

Attached to the underside of bottom wall 13 is a pipe 20 extending downwardly and closed by a plug 21 having a central opening 22. Pipe 20 is provided with an outlet drain pipe 23.

Extending upwardly through center hole 22 of plug 21 is a stainless steel pipe 24 which passes through a central opening 25in wall 15 and thereabove.

The pipe 24 extends below plug 21 and attached to its lower end is a T-fitting 26 having branches to which pipes 27, 28 are attached. Pipe 24 is welded to wall 15 as at 29.

On top of wall 15 is a stool piece or base 30 having a central opening 31 through which pipe 24 passes upwardly. Said base 30 has an outer upwardly extending flange 32. On base 30 is a cylindrical tube 33. The upper end of pipe 24 is located below the level of the upper end of tube 33. A ceramic tube 34 fits onto pipe 24 and rests on the base 30. The upper end of tube 34 is located just below the upper end of tube 24. Between pipe 34 and tube 33 are vertical, circular graphite felt layers 35. The layers 35 extend to a height just above the upper end of ceramic pipe 34 and rest on base 30. Mounted on the upper ends of layers 33 are circular discs 36 of graphite felt. Said discs form multi-layers and are disposed below the upper end of tube 33, and are formed with a central hole 37. The pipe 24 reaches said central hole 37.

Mounted on top of tube 33 is a pot 40 having an outer cylindrical wall 41 and a bottom wall 42 grooved at the periphery ofits underside, as at 42, to receive the upper end of tube 33. On top of pot 40 is a cover disc 43 formed with a central opening 44 at the center of an upwardly extending boss 45 formed with an outer downwardly divergent frusto-conical surface 46. The tube 33, pot 40 and lid 43 are of graphite.

Extending through walls 12, 16 and the waterjacket 17 is a horizontal pipe 50, the functions of which will be explained hereinafter. Also passing through walls 12, 16 and the water jacket 17 are three, equiangularly spaced, horizontal radiating tubes 51, the purpose of which will be hereinafter explained.

On top of walls l2, 16 is a top closure 52 for the container 11. Said closure 52 comprises a circular wall 53 mounted on ring 18 and formed with a central opening 54, and with an offset opening 55. Fitted onto wall 53 is a water jacket forming member 56 comprising a top wall 57 from which a cylindrical flange 58 extends downwardly contacting and attached to the periphery of wall 53, and attached at its lower end edge to the ring 18. Wall 57 has an opening 57a aligned with opening 55. Between walls 53 and 57 is formed a water jacket 60. Extending from flange 58 is a water drain pipe 61. Top wall 57 has a central hole 62 aligned with opening 54. Extending through openings 54, 62 is a short vertical pipe 63 extending from the underside of wall 53 to above wall 57. Pipe 63 is sealed to walls 53,57.

At the upper end of pipe 63 is a diameter same as pipe 63, frusto-conical surface 65.

At the upper end of pipe 64 is a flange 66 having a central hole 67 which may be of an inner diameter somewhat less than the inner diameter of pipes 63, 64. Flange 66 has bolt holes 68.

pipe 64 having an inner and an outer upwardly divergent Mounted on flange 66 is a colled port 69 comprising a lower flange 70 having bolt holes 71 registering with bolt holes 68 to receive attaching bolts. Welded to the flange 70 are inner and outer concentric tubes 73, 74, respectively forming a water jacket 75 therebetween. Welded to the upper end of said tubes 73, 74 is an upper flange 76. Extending from the lower end of tube 74 is a water inlet pipe 78. Attached to the upper end of tube 74 is a nipple 79. Surrounding the outer tube 74 is a tube of rubber or other heat insulating material. Outlet nipple 79 is connected by pipe 81 to an inlet nipple 82 leading to water jacket 60.

Mounted on boss 46 of lid or cover 43 is a graphite chimney 85. The lower end of chimney has an internal beveled surface 86 resting on conical surface 46. Said chimney 85 passes upwardly through pipes 63, 64 and through the cooled port 69 and thereabove. A thermo-couple 86a passes down through graphite pipe 85 and opening 44 into the pot 40. The opening 44 is of greater diameter than the thermo-couple 86a.

Disposed within the container 11 is an insulating chamber 90. Said chamber 90 comprises a cylindrical wall 91 surrounding the pot 40 and comprising an outer perforated stainless steel cage 92 with graphite felt layers 93 at its inside attached to said cage by moly clips 94 which pass through holes 95 in the cage 92. Any other suitable attaching means may be employed.

At the lower end of cage 92 and attached thereto, is a circular horizontal perforated stainless steel disc 96 formed with an opening 97 through which tube 33 passes and which is located above base 30. On disc 96 are flat layers 99 of graphite felt.

At the upper end of cage 92 is a perforated stainless steel disc 100 disposed above pipes 50, 51 and located below wall 53 and formed with a central opening 101 through which graphite chimney 85 passes. Attached to the underside of disc 100 are layers 102 of graphite felt. These may be attached by moly clips or in any other suitable manner.

Extending through pipes 51 are electric heating elements 104. Said heating elements pass through openings 104a in chamber 90. Openings 104a are larger than the heating elements. Hung from these heating elements and located in the chamber, are heating units 105 such as made by C. I. Hayes Inc. of Cranston, Rhode Island for electric heat treating vacuum furnaces. The units 105 comprise graphite cloth pieces 106 to the lower ends of which, arcurate weighted members 107 are attached.

Extending through openings 55 and 57a of walls 53, 57 of member 52, is a vertical tubular bearing 110. Extending through said bearing 110 is a vertical axle 111 of a crank member 112. At the upper end of axle 111 is a radial handle 113. Fixed to the lower end of axle 111 is a plate 114 of somewhat elliptical shape. In FIGS. 1 and 2, the plate 114 is offset from opening 54. Plate 114 comprises a top layer 114a of metal such as Inconel 600 and four layers 114b of graphite felt cemented to layer 114a and to each other by graphite cement. Plate 114 has a through hole 115 smaller than but centralized with respect to pipe 63 in the position of FIG. 4 (with the graphite chimney 85 and the thermo-couple 86a removed).

Piping for supplying gases to the furnace and for creating vacuum is illustrated in FIG. 5. As shown, pipe 24 is connected to pipes 27, 28. Pipe 27 is connected through a hydrogen solenoid valve (to control flow of hydrogen to the pot 40), to pipe 121 in which is interposed a hydrogen flow meter 122 (to measure flow of hydrogen to pot 40). Pipe 122 passes to a hydrogen shut off valve 123 (to shut off flow of hydrogent to pot 40), to pipe 124 which leads to a hydrogen supply. Instead of pure hydrogen, dissociated ammonia may be used. The dissociated ammonia comprises about 75 percent hydrogen and about 25 percent nitrogen.

Pipe 27 is connected through an argon solenoid valve 125 (to control flow of argon to pot 40), to pipe 126 connected to an argon flow meter 127 (to measure flow of argon to pot 40), which in turn is connected to pipe 128. Pipe 128 connects to an argon shut off valve 129 (to shut off flow of argon to pot 40) which is connected to pipe 130 connected to pipe 131 leading to a supply of argon.

Pipe or port 50 is connected through pipe 132 to a helium cool down valve 135 which in turn is connected by pipe 136 to helium supply 137.

Pipe 50 is connected by pipe 138 to pipe 139 connected to an argon bleed valve 140, which in turn is connected through pipe 141 to the argon supply pipe 131. Pipe 139 is also connected to pipe 142 which connects to an argon solenoid valve 144. Valve 144 connects to pipe 145 which connects to argon valve 147. Valve 147 connects to pipe 148 which connects to an argon flow meter 149. Said meter 149 connects to pipe 150 which connects to pipes 141, 131. An argon pressure switch 152 connects through pipe 153 to said pipe 150.

Pipe 138 connects to a pipe 154 which connects to a high vacuum valve 155. Valve 155 connects to pipe 156 which connects to a boaster pump 157. Said booster pump connects through pipe 158 to a pipe 159. Pipe 159 connects to a foreline valve 160 which connects through pipe 161 to a pipe 162. Pipe 162 connects to a rough line valve 163 to a pipe 164 which connects to pipes 138, 154.

Pipes 158, 159 connect through pipe 165 to a hold line valve 166. Said valve 166 is connected to pipe 167 which connects to solenoid valve 168. Said valve 168 is connected through pipe 169 to a holding pump 170.

Pipes 161, 162 are connected through pipe 171 to a mechanical pump 172.

The compacts or parts to be heat treated are placed on pans 181 which are stacked in spaced relation in the pot 40 by means of spacers 128. The pans 181 have center holes 183 which are aligned with hole 44.

The pans 181 with the parts 180 thereon may be stacked in pot 40 to the top.

At the beginning, the graphite chimney and thermo-couple are in place as shown in FIG. 1. Hydrogen is flowed through pipe 27 to pipe 24, but supply of argon to pipe 24 is shut off. Argon is supplied to port or pipe 50 at the same time.

The metal powders (tungsten carbide) are compacted as usual, cold, in order to make a part out of them. As the press friction is very great, the metal contain a lubricant or binder such as paraffin.

Heretofore, a pre-sintering was performed in either a hydrogen furnace of a vacuum furnace. The sintering process was also performed in a hydrogen furnace or a vacuum furnace. However, the part first went entirely through the presintering cycle including pre-heat, heat, and cool down, and when it cooled to room temperature, it was transferred to a sintering furnace for the sintering cycle. It was difficult to get rid of all the waxes which were trapped.

In accordance with the present invention the de-waxing in hydrogen and sintering in vacuum is accomplished in the single vessel without transfer.

There is also on the market a furnace which heat treats compacts in a vessel with various chambers, done in a vacuum chamber, but the compact has to be moved from one area to another to perform the various functions.

In the present invention, an atmospheric de-waxing operation is performed in hydrogen, and the same vessel is used for vacuum sintering without moving the part to be heat treated and in one continuous operation.

The cycle of the operation of the apparatus described is as follows: The chamber 90 is filled with argon. The argon enters container 11 through pipe or port 50 and passes through openings 104a into chamber 90. The inner pot 40 is filled with hydrogen. As the temperature increases, the parts will be dewaxed. The waxes will volatalize and pass up to the atmosphere through the graphite chimney 85. The argon protects the graphite components from oxidizing by excluding the air. The argon pressure is heavier than air and protects the elements.

The hydrogen burning at the top of the graphite chimney thereby burning the volatalized waxes. No air can mix so that the hydrogen burns and puts the wax vapors into the atmosphere. The de-waxing is carried out at about 400 C. The hydrogen prevents oxidation of the compacts.

The liberated wax would break down if it contacted the heating elements. With the present apparatus this is avoided by keeping the waxes separate so that they cannot reach the heating elements.

When temperature has been reached where all waxes have been volatalized, the supply of hydrogen to the pot is shut off and argon is flowed into the pot. The flushed out hydrogen burns at the top.

Argon is now inside of the pot and outside of the pot, and the temperature is still at 400 C. When the hydrogen flame goes out we know that argon is in the pot.

The graphite tube 85 and the thermo-couple 860 are now removed through the water cooled port 69, and a sight glass 190 will be placed over the port (FIG. 4), with an O-ring 191, placed between the sight glass and the upper surface of flange 76. Then all argon flow will be stopped through pipes 50 and 28.

The vacuum system will then be started and argon will be pumped out or exhausted from the chamber and pot. A vacuum suitable for sintering the compact will be achieved by means of the mechanical pump 172 and booster pump 157, the holding pump 170 being merely used to protect the booster pump.

The electric input to the heating elements is increased when the prescribed vacuum pressure has been achieved. At about 750 the compacts are presintered and at about 1,450 C. the compacts are sintered. The presintering is accomplished as the temperature rises from the de-waxing temperature to the sintering temperature. There is no cool-down between presintering and sintering. It is not necessary because the parts are not handled between de-waxing and sintering.

The flow of cooling water in jacket 75 and the provision of the rubber heat insulating tube 80 on the tube 74 keep the port 69 cool. The condensible gases flowing up are attracted to the inside surface of tube 73 and keeps the sight glass 180 from clouding up.

Thus the cooled port has two functions.

1. It keeps the graphite chimney cool and stops it from oxidizing (while the chimney is in place); and

2. Under vacuum operation, when the graphite chimney has been removed, and the sight glass has been installed, the sight glass is prevented from clouding up by preventing condensible vapors from settling on the sight glass and clouding it thereby preventing actual temperature readmg.

The operator looking down through the sight glass and through opening 183 in pans 181 can observe the color to judge the temperature.

After sintering is completed, and the heating units turned off, the compacts may be cooled by supplying helium to the pipe 50 from the helium supply 137.

It will thus be seen that there is provided an article in which the several objects of this invention are achieved, and which is well adapted to meet the conditions ofpractical use.

As possible embodiments might be made of the above invention, and as various changes might be made in the embodiments above set forth, it is to be understood that all matter herein set forth or shown in the accompanying drawings, is to be interpreted as illustrative only.

lclaim:

1. Apparatus for heat treating powder metal compacts comprising a vessel in which the compacts are placed, means to provide a passage from the vessel to the air, means to supply a flow of an atmospheric gas to the vessel, which will exclude air from the vessel, means to heat the vessel to a temperature to volatalize waxes from the compacts, said gas causing the volatalized waxes to flow out of said passage with said gas and burn in the air, while said gas in the vessel excludes air from entering the interior of the vessel through said passage so as to prevent oxidizing the compacts within said vessel while said compacts are being de-waxed, means for creating a vacuum in said vessel and means to raise the temperature of the heat in the vessel to sintering temperature to sinter the compacts in vacuum and without removing said compacts from said vessel.

2. The combination of claim 1, means to shut off supply of said atmospheric gas to said vessel, means for supplying an inert gas to said vessel and means to shut off supply of said inert gas to said vessel before operating the means to create vacuum in said vessel.

3. The combination of claim 2, a heat insulating chamber in which said vessel is located, and means to supply inert gas to said chamber while said atmospheric gas is being supplied to said vessel.

4. The combination of claim 3, and means to shut off supply of inert gas to said chamber when supply of inert gas to said vessel is shut off.

5. The combination of claim ll, said prising hydrogen.

6. The combination of claim 3, said inert gon.

7. Apparatus for heat treating powdered metal compacts comprising a heat insulating chamber, a pot in which the compacts to be heat treated are placed, said pot being disposed in said chamber, said pot having a hole, means to provide a passage from the hole to the atmosphere, means to heat said pot, means to supply gas comprising hydrogen, the said pot, means to supply an inert gas to said chamber, means to shut off said supply of said hydrogen comprising gas to said pot, means to supply inert gas to said pot, means to shut off said supply of inert gas to said chamber, means to shut off said supply of said inert gas to said pot, and means to create a vacuum in said chamber and pot and means to raise the temperature of said heat means to sintering temperature.

8. The combination of claim 7, said means to provide a passage from said hold in said pot to the atmosphere, being removable to establish communication between said chamber and pot through said hole.

9. The combination of claim 8, and means to cool said passage providing means, outside of said chamber.

10. The combination of claim 9, said passage providing means comprising a graphite chimney resting on said pot, and communicating with said hole in said pot, said means to cool said passage providing means, comprising a water jacket surrounding said chimney.

11. The combination of claim 10, and an insulating tube surrounding said waterjacket.

12. The combination of claim 11, and a sight glass mountable on the upper end of said water jacket upon removing said chimney.

13. The combination of claim 7, and a water cooled container surrounding said chamber.

14. The combination of claim 13, said container having an opening through which said passage providing means passes.

15. The combination of claim 14, said passage providing means being removable, and movable means on the container to cover said opening in said container when said passage providing means is removed, said cooler means having a peep hole aligned with said hole in said pot when in position covering said opening.

16. The combination of claim 14, and a water cooled jacket on top of said container surrounding said opening in said container, said passage providing means comprising a removable graphite chimney passing through said water jacket and opening, and resting on said pot and surrounding said hole in said pot.

17. The combination of claim 7, and means to provide a cooling gas to the inside of said chamber.

18. The combination of claim 1, the passage from the vessel to the air comprising a chimney extending from the upper end of the vessel to the air.

19. The combination of claim 18, the means to supply atmospheric gas to the vessel comprising an atmospheric gas supply pipe connected to the lower end of said vessel and communicating therewith.

atmospheric gas comgas comprising ar- 

2. The combination of claim 1, means to shut off supply of said atmospheric gas to said vessel, means for supplying an inert gas to said vessel and means to shut off supply of said inert gas to said vessel before operating the means to create vacuum in said vessel.
 3. The combination of claim 2, a heat insulating chamber in which said vessel is located, and means to supply inert gas to said chamber while said atmospheric gas is being supplied to said vessel.
 4. The combination of claim 3, and means to shut off supply of inert gas to said chamber when supply of inert gas to said vessel is shut off.
 5. The combination of claim 1, said atmospheric gas comprising hydrogen.
 6. The combination of claim 3, said inert gas comprising argon.
 7. Apparatus for heat treating powdered metal compacts comprising a heat insulating chamber, a pot in which the compacts to be heat treated are placed, said pot being disposed in said chamber, said pot having a hole, means to provide a passage from the hole to the atmosphere, means to heat said pot, means to supply gas comprising hydrogen, the said pot, means to supply an inert gas to said chamber, means to shut off said supply of said hydrogen comprising gas to said pot, means to supply inert gas to said pot, means to shut off said supply of inert gas to said chamber, means to shut off said supply of said inert gas to said pot, and means to create a vacuum in said chamber and pot and means to raise the temperature of said heat means to sintering temperature.
 8. The combination of claim 7, said means to provide a passage from said hold in said pot to the atmosphere, being removable to establish communication between said chamber and pot through said hole.
 9. The combination of claim 8, and means to cool said passage providing means, outside of said chamber.
 10. The combination of claim 9, said passage providing means comprising a graphite chimney resting on said pot, and communicating with said hole in said pot, said means to cool said passage providing means, comprising a water jacket surrounding said chimney.
 11. The combination of claim 10, and an insulating tube surrounding said water jacket.
 12. The combination of claim 11, and a sight glass mountable on the upper end of said water jacket upon removing said chimney.
 13. The combination of claim 7, and a water cooled container surrounding said chamber.
 14. The combination of claim 13, said container having an opening through which said passage providing means passes.
 15. The combination of claim 14, said passage providing means being removable, and movable means on the container to cover said opening in said container when said passage providing means is removed, said cooler means having a peep hole aligned with said hole in said pot when in position covering said opening.
 16. The combination of claim 14, and a water cooled jacket on top of said container surrounding said opening in said container, said passage providing means comprising a removable graphite chimney passing through said water jacket and opening, and resting on said pot and surrounding said hole in said pot.
 17. The combination of claim 7, and means to provide a cooling gas to the inside of said chamber.
 18. The combination of claim 1, the passage from the vessel to the air comprising a chimney extending from the upper end of the vessel to the air.
 19. The combination of claim 18, the means to supply atmospheric gas to the vessel comprising an atmospheric gas supply pipe connected to the lower end of saId vessel and communicating therewith. 